Forests are being converted to agriculture throughout the Afrotropics, driving declines in sensitive rainforest taxa such as understorey birds. The ongoing expansion of cocoa agriculture, a common small‐scale farming commodity, has contributed to the loss of 80% rainforest cover in some African countries. African cocoa farms may provide habitat for biodiversity, yet little is known about their suitability for vertebrate fauna, or the effect of farm management on animal communities. Here, we report the first in‐depth investigation into avian diversity and community composition in African cocoa, by assembling a dataset of 9,566 individual birds caught across 83 sites over 30 years in Southern Cameroon. We compared bird diversity in mature forest and cocoa using measures of alpha, beta and gamma diversity, and we investigated the effect of cocoa farm shade and forest cover on bird communities. Gamma diversity was higher in cocoa than forest, though alpha diversity was similar, indicating a higher dissimilarity (beta diversity) between cocoa farms. Cocoa farms differed from forest in community composition, with a distinctive decrease in relative abundance of insectivores, forest specialists and ant‐followers and an increase in frugivores. Within cocoa farms, we found that farms with high shade cover in forested landscapes resulted in higher relative abundance and richness of sensitive forest species; shady farms contained up to five times the proportion of forest specialists than sunny farms.
Bird conservation in agricultural settings can be controversial. While some bird species damage some crops, others suppress insect pests. Few studies have simultaneously compared bird services and disservices to assess their net impact. Using an exclusion experiment in six California strawberry farms, we show that bird suppression of berry damage by insect pests (about 3.8% of berries) is similar in magnitude to the damage birds inflict on strawberries (about 3.2% of berries). Across 27 farms, we found that bird species richness and the relative abundance of insectivorous birds increased, while the relative abundance of strawberry‐eating birds and bird damage decreased on farms with more semi‐natural land cover in the surrounding landscapes (1000 m radius). Relative to homogeneous farms, those that implemented diversification practices, such as hedgerows, flower strips or increased crop diversity, had greater bird species richness, total relative abundance, insectivore abundance and strawberry‐eating bird abundance.
- NSF-PAR ID:
- 10460158
- Publisher / Repository:
- Wiley-Blackwell
- Date Published:
- Journal Name:
- Journal of Applied Ecology
- Volume:
- 56
- Issue:
- 8
- ISSN:
- 0021-8901
- Page Range / eLocation ID:
- p. 1948-1959
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
More Like this
-
more » « less
Abstract Synthesis and applications . Sunny African cocoa farms were less able to support sensitive bird guilds compared with shaded farms in forested landscapes. Our findings support the notion that certain ecological and dietary guilds, such as ant‐followers and forest specialists are disproportionately affected by land‐use change. In light of the current push to increase cocoa production in sub‐Saharan Africa, our results provide policymakers opportunities for more wildlife‐friendly cocoa schemes that maximize avian diversity. -
more » « less
Abstract The conversion of biodiversity‐rich woodland to farmland and subsequent management has strong, often negative, impacts on biodiversity. In tropical smallholder agricultural landscapes, the impacts of agriculture on insect communities, both through habitat change and subsequent farmland management, is understudied. The use of agroecological practices has social and agronomic benefits for smallholders. Although ecological co‐benefits of agroecological practices are assumed, systematic empirical assessments of biodiversity effects of agroecological practices are missing, particularly in Africa.
In Malawi, we assessed butterfly abundance, species richness, species assemblages and community life‐history traits on 24 paired woodland and smallholder‐managed farmland sites located across a gradient of woodland cover within a 1 km radius. We tested whether habitat type (woodland vs. farmland) and woodland cover at the landscape scale interactively shaped butterfly communities. Farms varied in the implementation of agroecological pest and soil management practices and flowering plant species richness.
Farmland had lower butterfly abundances and approximately half the species richness than woodland. Farmland butterfly communities had, on average, a larger wingspan than woodland site communities. Surprisingly, higher woodland cover in the landscape had no effect on butterfly abundance in both habitats. In contrast, species richness was higher with higher woodland cover. Butterfly species assemblages were distinct between wood‐ and farmland and shifted across the woodland cover gradient.
Farmland butterfly abundance, but not species richness, was higher with higher flowering plant species richness on farms. Farms with a higher number of agroecological pest management practices had a lower abundance of the dominant butterfly species, but not of rarer species. However, a larger number of agroecological soil management practices was associated with a higher abundance of rarer species.
Synthesis and applications : We show that diversified agroecological soil practices and flowering plant richness enhanced butterfly abundance on farms. However, our results suggest that on‐farm measures cannot compensate for the negative effects of continued woodland conversion. Therefore, we call for more active protection of remaining African woodlands in tandem with promoting agroecological soil management practices and on‐farm flowering plant richness to conserve butterflies while benefiting smallholders. -
more » « less
Abstract In the tropics, smallholder farming characterizes some of the world's most biodiverse landscapes. Agroecology as a pathway to sustainable agriculture has been proposed and implemented in sub‐Saharan Africa, but the effects of agricultural practices in smallholder agriculture on biodiversity and ecosystem services are understudied. Similarly, the contribution of different landscape elements, such as shrubland or grassland cover, on biodiversity and ecosystem services to fields remains unknown.
We selected 24 villages situated in landscapes with varying shrubland and grassland cover in Malawi. In each village, we assessed biodiversity of eight taxa and ecosystem services in relation to crop type, shrubland and grassland cover and the number of agroecological pest and soil management practices on smallholder's fields of different crop types (bean monoculture, maize‐bean intercrop and maize monoculture).
Increasing shrubland cover altered carabid and soil bacteria communities. Carabid abundance increased in maize but decreased in intercrop and bean fields with increasing shrubland cover. Carabid abundance and richness and wasp abundance increased with soil management practices. Carabid, spider and parasitoid abundances were higher in bean monocultures, but this was modulated by surrounding shrubland cover. Natural enemy abundances in beans were especially high in landscapes with little shrubland, possibly leading to lower bean damage in monocultures compared to intercropped fields, whereas maize monocultures had higher damage. In maize, grassland cover and pest management practices were positively related to damage. Carabid abundance was higher fields with high bean damage, and increased carabid richness in fields with high maize damage. Parasitoid abundance was negatively associated with bean damage.
Synthesis and application . Our results suggest that maintaining biodiversity and ecosystem services on smallholder farms is not achievable with a ‘one size fits all’ approach but should instead be adapted to the landscape context and the priorities of smallholders. Shrubland is important to maintain carabid and soil bacterial diversity, but legume cultivation beneficial to natural enemies could complement pest management in landscapes with a low shrubland cover. An increased number of agroecological soil management practices can lead to improved pest control while the effectiveness of agroecological pest management practices needs to be re‐evaluated. -
more » « less
Abstract Thresholds in the relationship between species richness and natural land cover can inform landscape‐level vegetation protection and restoration targets. However, landscapes differ considerably in composition and other environmental attributes. If the effect of natural land cover on species richness depends on (i.e., interacts with) these attributes, and this affects the value of thresholds in this relationship, such dependencies must be considered when using thresholds to guide landscape management.
We hypothesized that the amount of natural land cover at which a threshold occurs would differ in predictable ways with particular anthropogenic, abiotic, and biotic attributes of landscapes. To test this, we related woodland bird species richness in 251 landscapes, each 100 km2, to natural land cover in south‐east Australia. We compared the fit of exponential and threshold models of the richness–natural land cover relationship, focussing on the extent of natural land cover at which thresholds presented among landscapes that differed in matrix land use intensity, heterogeneity, productivity, and the prevalence of strong biotic interactors. We used linear mixed modelling to examine how interactions between natural land cover and the various landscape attributes affected the fit of models of species richness.
Threshold models of the richness–natural land cover relationship were always a better fit than exponential models. Threshold values did not vary consistently with specific landscape attributes, with the exception of landscapes that were classified by the prevalence of strong biotic interactors (hypercompetitive native birds of the genus
Manorina ).Natural land cover had a more positive effect on species richness in landscapes when
Manorina prevalence was higher. This positive interaction provided the biggest improvement in explanatory power of models of species richness.Synthesis and applications . While we detected an interaction betweenManorina prevalence and the area of natural land cover, generalities relating to the underlying nature of thresholds in the richness–natural land cover relationship remain elusive. Complex interactions, relating to various landscape attributes and associated ecological processes, likely underpin variation in threshold values. Until these complexities are better understood, the use of thresholds for informing landscape management and conservation target setting should be approached with caution. -
more » « less
Abstract Birds increase crop yields via consumption of pests in some contexts but disrupt pest control via intraguild predation in others. Landscape complexity acts as an inconsistent mediator, sometimes increasing, decreasing, or not impacting pest control. Here, we examined how landscape context and seasonal variation mediate the impact of birds on arthropod pests and natural enemies, leaf damage, and yields of broccoli (Brassica oleracea) on highly diversified farms that spanned the USA west coast. Our study had two complementary components: a bird exclusion experiment and molecular diet analysis of 357 fecal samples collected from the most commonly captured bird species that also foraged in Brassica fields—American Goldfinch (Spinus tristis), American Robin (Turdus migratorius), Savannah Sparrow (Passerculus sandwichensis), Song Sparrow (Melospiza melodia), and White-crowned Sparrow (Zonotrichia leucophrys). Bird access yielded higher, rather than lower, numbers of pest aphids and increased their parasitism, while no other arthropods examined were consistently impacted. Independent of bird presence, percent natural cover in the landscape sometimes increased and sometimes decreased densities of arthropods in the mid-growth period, with diminishing impacts in the late-growth period. Herbivore feeding damage to broccoli leaves decreased with increasing amounts of natural land cover and in the late-growth period. Molecular diet analysis revealed that Brassica pests and predatory arthropods were relatively uncommon prey for birds. Landscape context did not alter the prey items found in bird diets. Altogether, our bird-exclusion experiment and molecular diet analysis suggested that birds have relatively modest impacts on the arthropods associated with broccoli plantings. More broadly, the limited support in our study for net natural pest control services suggests that financial incentives may be required to encourage the adoption of bird-friendly farming practices in certain cropping systems.
